The present invention relates to the dissemination and reception of location data intended for entities with short-range receivers.
A number of technologies exist for the short range communication of information between mobile devices. These technologies include infra-red based technologies and low-power radio technologies (including, in particular, the recent xe2x80x9cBluetoothxe2x80x9d short range wireless standard). Depending on the technology implementation, differing types of message propagation will be enabled including asynchronous message broadcast, and multicast and point-to-point duplex connections established after coordination and negotiation between communicating devices.
One possible use for such short-range technologies is the transmission of local information to passers-by equipped with mobile devices having short-range transceivers, the local information being, for example, transmitted by a shop to inform the passers-by of current promotions. Another use is in location beacons that transmit location information to passers-by.
It is known, for example from EP-A-0,948,222, to diffuse information amongst users by short range wireless links so that a user need not be in range of an originating transmitter in order to receive the information sent out by the latter. The process of diffusion takes advantage of both the short range wireless technology and the movement of the users carrying the devices. Such an arrangement is likely to be particularly useful in environments such as shopping malls, city centers, tourist attractions, theme parks or any other location where large numbers of users carrying mobile devices with short-range transceivers are likely to be in one locality. Another important area of application is the diffusion of information between devices fixed in cars.
By applying appropriate diffusion-limiting mechanisms (for example, by assigning the original information a total time to live of, for example, 10 minutes), the information can be restricted to the vicinity of the originating point 10. This makes the diffusion process appropriate for the diffusion of location relevant information that is primarily of use only in the vicinity of point 10.
The diffused information can, of course, include the location of the originating point. For devices receiving the information directly from the originating point, this provides them with a fairly accurate indication of their location (because the information is received over a short-range link). However, as the information is diffused between devices, the newly-receiving devices get less and less accurate location information.
Our co-pending European Application 01301826.2 describes a method by which an entity receiving location data by diffusion from several different sources, can use this data to estimate its current position in dependence on the relative prominence of the sources.
Our co-pending European Application EP 01305936.5 describes another method by which an entity can discover its location using multiple items of location data received by short-range diffusion from several sources. In this method, each location data item includes an indication of the distance traveled by the location data item from its source, either by displacement of entities temporarily holding the item or by transmission. This distance represents an upper bound on the current distance of a receiving entity from the source concerned and this can be used, together with upper-bound distances from other sources, to discover a current zone where the entity is likely to be located; various averaging techniques can then be applied to derive a current location for the entity.
However, having a receiving entity continuously powered up ready to receive any location data broadcast within range is undesirable in the case of battery-powered receiving entities as this significantly reduces battery life. Accordingly, it is an object of the present invention to reduce the power consumption of a receiving entity without unduly reducing the amount of location data likely to be received.
According to one aspect of the present invention, there is provided apparatus comprising:
a short-range receiver for receiving location data, the receiver having an activated state in which it is operative to receiver location data and a de-activated state in which at least a substantial portion of the receiver is powered down;
a clock subsystem including an input arrangement for receiving reference-time data indicative of a time reference external to the apparatus, and a clock responsive to received reference-time data to keep an internal timing substantially coordinated with said time reference;
a wake-up subsystem for placing the receiver in its activated state at predetermined times relative to said internal timing; and
a location-data handling subsystem for handling location data received by the receiver.
The receiver is thus woken up at specific times with respect to the time reference, these times being chosen to be when location data is most likely to be available. As a result, power consumption is reduced which is of particular advantage for battery-powered mobile devices.
According to another aspect of the present invention, there is provided a method of disseminating location information to devices equipped with short-range receivers, the method comprising the steps of:
disseminating reference time data for establishing a common timing reference across multiple items of equipment;
transmitting location information by short-range communication at known times relative to said common timing reference;
receiving said reference time data at a device and using it to synchronise an internal clock with said common timing reference; and
powering up a short-range receiver of the device at said known times relative to the common timing reference as represented by the internal clock, in order to receive location information.
According to a further aspect of the present invention, there is provided a location system for mobile devices, comprising:
an arrangement for disseminating absolute time;
location-disseminating means for receiving absolute time information from said arrangement and for transmitting location information at fixed absolute times;
mobile devices for receiving and maintaining absolute time information from said arrangement and for powering up for short time windows to receive location information transmitted at said fixed absolute times.
The infrastructure used to provide the location data can also be used by apparatus that does not have a need to save power by powering down its receiver; however, in this case measures are preferably taken to minimise or prevent message transmission that would conflict with the location data transmissions. Thus, according to a still further aspect of the present invention, there is provided apparatus comprising:
a short-range transceiver;
a location-data handling subsystem for handling location data received by the transceiver;
a timing subsystem including an input arrangement for receiving reference-time data indicative of a time reference external to the apparatus, and a time-window determining arrangement for determining, with respect to said time reference, the occurrence of location-data time windows that are scheduled to occur at known times relative to said time reference; and
a send control for managing the sending of messages by the apparatus using the transceiver, the send control being operative to minimise or eliminate the sending of messages during said location-data time windows determined by the determining arrangement.